HD Blog

Anticipation. One issue to consider in testing of asymptomatic at-risk individuals is anticipation, the phenomenon in which there is increasing disease severity or decreasing age of onset in successive generations. Anticipation occurs more commonly in paternal transmission of the mutated allele [Ridley et al 1988 , Ridley et al 1991]. The phenomenon of anticipation arises from instability of the CAG repeat during spermatogenesis [Duyao et al 1993 , Telenius et al 1995]. Large expansions in CAG repeat size [>7 CAG repeats] occur almost exclusively through paternal transmission. Most often children with juvenile-onset disease have inherited the expanded allele from their fathers.

DNA banking. DNA banking is the storage of DNA (typically extracted from white blood cells) for possible future use. Because it is likely that testing methods and our understanding of genes, mutations, and diseases will improve in the future, consideration should be given to banking DNA particularly when interpretation of results is difficult. For example, if an affected family member is not available or chooses not to be tested, interpretation of a "negative" result in at risk family members is difficult. An affected family member who chooses not to be tested may be willing to have DNA banked for future use by other family members. See DNA Banking for a list of laboratories offering this service.